The corepressor nuclear receptor (CORNR) box is found in the N-CoR and SMRT corepressors of nuclear receptors (NRs), and confers binding to NRs. Repression of NR regulated genes is mediated by histone deacetylated which are recruited by the N-CoR and SMRT corepressors. Both N-CoR and SMRT have two copies of the CORNR box. The consensus sequence is LxxxIxxxI/L. A structural analysis of the second CORNR box of SMRT bound to the AF-2 domain of PPARalpha shows the CORNR box is a 9 aa alpha-helix that is bound to the AF-2 domain groove of PPARalpha (Xu,2002), in a similar manner to the related NR box (ELM_ID:LIG_NRBOX) found in co-activators of NRs. However, preference for the CORNR box over the NR box is dictated by the exact conformation of the AF-2 domain. In the unliganded state (or when bound to agonist ligands), the AF-2 domain conformation of the NRs promotes binding of corepressors through the CORNR box. In this state, the NR boxes of coactivators does not fit into the groove (Jepsen,2002).